The Asymptomatic Carrier State in Families with Tinea Capitis

A 2.5 % Carrier Rate Identified in Tinea Capitis in Belgium

Tinea capitis (TC) is a superficial fungal infection affecting the scalp.

Microsporum canis is the most common agent identified in Europe whereas T. tonsurans is the most common in North America. Over time, more than more anthropophilic species are being identified in Europe. Children are most often affected by tinea capitis – possibly because the scalps of children have lower concentrations of so called ‘fungistatic fatty acids.

The “Asymptomatic Carrier”

Asymptomatic carriers  are defined as individuals in which dermatophytes are identified, even though no clinical signs are observed. These are often family members.  The existence of asymptomatic carriers (ACs) could represent a potential reservoir responsible of (re)contamination of the patient and failure of treatment.

As a reminder there are 3 important dermatophyte species anthropophilic, zoophilic and geophilic. In asymptomatic carriers,  anthropophilic species are predominant. These group of fungi often  adapt more easily to the host and induce a weaker immune response than the zoophilic fungi. In other words, they can hide easier without causing the host to take note of them. It’s difficult to predict what happens with a person who becomes an asymptomatic carrier. It’s possible for there to be spontaneous resolution, or the asymptomatic carriage state to persist for months or even years or for the patient to develop true infection (tinea capitis)

 Lecerf P et al. 2022

In this study, authors set out to assess the prevalence of ACs in a cohort of household contacts of children who were diagnosed with TC in the metropolitan area of Belgium. They point out that no prospective studies on ACs in household contacts of TC patients in Europe had been published to date. So what’s unique about this study is that it was prospective in nature.

 So this prospective observational study was conducted from October 2015 to April 2016. Patient and carriers had tinea capitis identified by KOH preparations as well as culture. There were 96 cases of tinea capitis from 95 different families. The main infectious agent of the actual patient was Microsporum audouinii in 53 cases. This was followed by T tonsurans in 16, T soudanese in 14, T violaceaum in 11 and M canis in 5. The mean age of TC patients was 5.8 years. Male/female ratio was 2.8.

Eighty-one household contacts of TC patients were enrolled in the study. Two cases of “asymptomatic carriers“ (representing 2.5%) were identified. Two ACs were identified (2.5%): 1 girl (with M. audouinii) and 1 boy (with Trichophyton tonsurans). Both carriers were aged less than 10 years.

DISCUSSION AND COMMENT

This is a nice study which captures data on an area of epidemiology that’s challenging to capture - data on healthy people that don’t always want to really be bothered bu participating in studies. The authors point out that there have been about 26 studies regarding the prevalence of asymptomatic carriers for tinea capitis have been published to date. What made this unique was that it was the first European prospective study on asymptomatic scalp carriage among household contacts of tinea capitis patients.

What was fascinating here is that that authors point out that the chances of asymptomatic carriage is all over the place and ranges from  0.3% to 97% in the literature. The authors noted that in Spain and Italy where tinea capitis has been relatively rare, the prevalence of scalp carriage was 0.2% and 0.3%, respectively. In contrast, the authors make note that a higher prevalence rates of around 49 % have been documented for asymptomatic carriage in South Africa where Trichophyton violaceum type tinea capitis is endemic. In the USA where T. tonsurans is prevalent, the carrier rates range from around 8% to up to 15%.

This study puts the number at 2.5 % in Belgium.

The final interesting point here relates to how difficult, frustrating and time consuming it is to screen family members.  Many family members decline screening and it’s difficult to track down family members. Despite, this efforts should be made to screen family members. Pets were not included in this study and we we need to keep in mind the need to screen widely in the case of zoophilic and geophilic fungi

REFERENCE

Lecerf P et al. Asymptomatic Scalp Carriage among Household Contacts of Children Affected by Tinea Capitis: A Prospective Study in the Metropolitan Area of Brussels, Belgium.  Skin Appendage Disord. 2022 May;8(3):200-205.